Bottom structure for plastic containers

ABSTRACT

A bottom structure for containers particularly suited for carbonated beverage bottles. The bottom end is formed with a domed center portion and an intersecting downwardly convexed semi-torus portion which is interrupted by a plurality of radially arranged rib configurations extending from the side wall of the bottle inwardly to the juncture of the aforesaid portions and form a plurality of downwardly bulged legs arranged in a rosette pattern and adapted to be loaded in bend in opposition to a compression loading on the dome portion when subjected to internal fluid pressure and heat to provide a novel creep resistant structure.

United States Patent Adomaitis BOTTOM STRUCTURE FOR PLASTIC CONTAINERSDomas Adomaitis, Chicago, Ill.

Continental Can Company, Inc., New York, NY.

Filed: Feb. 26, 1973 Appl. No.: 335,974

Inventor:

Assignee:

US. Cl. 215/1 C, 220/70 Int. Cl B65d 23/00 Field of Search 215/1 C;220/66, 70, 72

References Cited UNITED STATES PATENTS 6/1962 Daley ..220/70x 8/l97lAdomaitis ..215/1c Primary ExaminerWilliam 1. Price AssistantExaminer-Steven M. Pollard Attorney, Agent, or Firm-John J Kowalik;Joseph E. Kerwin; William A. Dittmann [57] ABSTRACT A bottom structurefor containers particularly suited for carbonated beverage bottles. Thebottom end is formed with a domed center portion and an intersectingdownwardly convexed semi-torus portion which is interrupted by aplurality of radially arranged rib configurations extending from theside wall of the bottle inwardly to the juncture of the aforesaidportions and form a plurality of downwardly bulged legs arranged in arosette pattern and adapted to be loaded in bend in opposition to acompression loading on the dome portion when subjected to internal fluidpressure and heat to provide a novel creep resistant structure.

8 Claims, 5 Drawing Figures a ii h l N/ l\ 1 a' :7 f; i W l l 3 j :4 1 gi 5 2a" t BOTTOM STRUCTURE FOR PLASTIC CONTAINERS DISCUSSION OF THEPRIOR ART The best art known is previous US. Pat. No. 3,598,270. Thestructure therein shown is satisfactory from a functional standpoint,but it has been found too expensive to manufacture necessitating anexpensive mold. Also the bottom is loaded solely in tension whichrequires deep rib conformations and required excessive use of material.This provides a rigid structure with deep grooves in the side wall atthe bottom end.

As stated in the prior art the duplication in plastic of glass bottlesis not feasible since plastic economically suitable for such bottles issubject to distortion and creep particularly when subjected totemperatures of l20 to 140F. as during pasteurization or on a hot summerday in enclosed vehicles or the like. Such plastic bottles mustwithstand pressures of 40 p.s.i. to in excess of I p.s.i. As heretoforenoted, the bottom end of the bottle is normally the weakest partnecessitated by manufacturing techniques and simply thickening thesection will not solve the problems enumerated particularly since theplastic bottle must be a substitute in general shape and capacity forcurrently used glass bottles, that is it must of necessity be ofsubstantially the same size not only to accept the same quantity ofbeverage but also to be handled by equipment currently in use.

Furthermore. the bottle must be aesthetically pleasing to the customeras well as being satisfactory functionally.

SUMMARY OF THE INVENTION Bottom bulging of a pressurized plasticcontainer is a serious problem. Such a container becomes a rocker" ormay loose completely its footing and tip over. Because of bottom bulgingvolume of the container increases and the fill line drops tounacceptable level.

It has been known for along time, that the strongest pressure vessel isone of a spherical shape. Its excellent performance is based on auniform distribution of stresses: tensile stresses in case of internalpressure and compressive stresses in case of external pressure. Sincespherical containers or those with hemispherical bottoms require extrastands or footing they are impractical for application such as beveragebottle.

Next to the hemispherical there is the domed bottom, which has abuilt-in up-side down hemisphere, a cone or construction between thetwo. However, under pressure domed bottoms bulge, too. Despite itsrigidity, the dome looses some of its depth and the base diameterdecreases. After these changes the bottle becomes also taller and not asstable.

The usual approach to solve the problem is to make the bottom heavy.

The approach of this invention is to use material where it is needed.

In looking for reasons of domed bottom bulging and instability theforces and stresses applied to the bottom in service, was analyzed. Theexternal pressure on a cone or hemisphere cannot decrease height ofthese constructions unless compressive strength of the wall would beexceeded and the walls would be compressed or the diameter andcircumference of its base would be increased.

At the lowermost wall of the bottom dome there is an area wherecompressive stresses are changing to flexural (bending) and tensilestresses. That critical area usually is the bottom rim or the adjacentbottom section. Since plastic material is weakest in tension, thecritical tensile stresses in this area are reached first and they arefollowed by critical flexural stresses before the critical compressivestresses can be expected. With this in mind the mechanism of the bottombulging, which is manifested mainly by a decreased dome height and basediameter, can be described.

The domed bottom is strong as long and/or where it is exposed tocompressive stresses only. However, at the area where the dome blendswith the bottom rim it is exposed to the most damaging tensile stresses.When these stresses become critical the area involved yields andelongates, thus giving a chance for bending stresses and partialinversion of the dome. Depth of the cone or dome can decrease only ifthe base diameter and circumference of the dome at these points elongateto allow bending of the lower section of the dome outwardly.

From the above analysis and description of bottom bulging mechanism itcan be concluded that in order to improve performance of the domebottom. reinforcement of its critical base section is needed. Thisfinding constitutes the core of my invention.

The purpose of the invention is to eliminate domed bottom bulging byproviding an integral reinforcing rim at its base in order:

1. to expose the bottom dome to compressive stresses only;

2. to arrest the tensile and bending stresses at the base of the dome;

3. to cut excessive material from the dome and to produce a moreeconomical plastic container.

The present invention is directed to a bottle particularly adapted foruse with carbonated beverages.

A general object of the invention is to provide a novel bottom endportion for a plastic bottle wherein the end portion is contoured toplace certain sections in compression and others in bend in a unifiedconstruction which utilizes the least amount of material, obtains astable product, aesthetically is acceptable and pleasing and is capableof either blow molding or injection blow molding.

A further object is to provide a novel bottom conformation for acontainer easy to manufacture and provides the necessary strengthdeveloped by a novel arrangement of wall components including a domedcenter portion and an encompassing rim portion with which it isintegrated and at its outer edge merges with the outer side wall, therim portion being formed with a plurality of rib formations which extendfrom the juncture of the rim with the dome portion to and beyond thejuncture of the rim portion with the side wall.

These and other objects and advantages inherent in and encompassed bythe invention will become more readily apparent from the specificationsand drawings, wherein:

FIG. I is a side elevational view of a bottle incorporating theinvention;

FIG. 2 is an end view of the bottom;

FIG. 3 is a transverse longitudinal sectional view taken substantiallyon line 33 of FIG. 1;

FIG. 4 is a partial sectional view taken essentially on line 4-4 of FIG.2'. and

FIG. is a sectional view taken substantially on line 5-5 of FIG. 1.

DESCRIPTION OF THE INVENTION Describing the invention in detail there isshown a plastic bottle generally designated 2 suitable for carbonatedbeverages. The material used may be of the type identified as DuPontNR-16 or Barex 2IO sold by Vistron Corporation located in Ohio or anyother like suitable material. Although such bottles represent aprincipal application of the invention, it will be understood that theinvention is applicable to containers generally.

The bottle comprises an upper end neck portion 3 which blends into abody comprising a side wall portion 4 having at least a bottom section 5of cylindrical configuration. The lower edge of the cylindrical sectionblends into a bottom wall structure 7 which essentially extendstransaxially of the bottle.

The bottom section comprises a center dome portion 8 which has a convexupper side 9 internally of the body and a concave underside 10.

The dome portion 8 merges at its lower edge into the inner edge of a rimsection II which is in the form of semitorus or half a donut, the outeredge of which merges into the lower section of the cylindrical wallportion 5.

The rim section is generally U shaped in crosssection and has a concaveinner side 12 and a convex outer or bottom side 13.

A series of regularly spaced ribs or reinforcing elements 14,14 areprovided between legs 15,15 in the rim portion.

Each rib I4 is U-shaped in transverse cross-section and comprises sidewebs 16,16 which grow thicker inwardly and merge into a crest or ridgeportion 17 of relatively thicker section. The side edges 18,18 of theribs diverge slightly radially outwardly and define the margins of anintervening groove 19.

The inner and outer ends 20 and 21 of the grooves converge toward theirextremities and shallow out and blend into the dome wall and the sidewall respectively.

It will be noted that the ribs are of widest formation circumferentiallyof the container at 22 in the corner 23 formed by the juncture of thebottom and side walls of the container.

Thus strength is imparted at a critical area to resist bending momentsimposed by the compressive loading of the dome portion.

The ribs are convexed inwardly of the container and have concave bottomsides forming the grooves.

Each leg portion has a base pad section 25 which extends laterally, thatis, circumferentially of the container side webs of adjacent ribstructures and merges therewith in inturned rounded surfaceconfigurations. In longitudinal section, that is, radially of thecontainer, the legs are of U-shaped convexed outwardly and provide atsaid pad sections 25 coplanar seating areas for the bottle.

The instant structure has been tested at I40F. for two hours and hasperformed satisfactorily.

What is claimed is:

I. A blow molded pressure resistant plastic container having a bodycomprising a generally cylindrical side wall and a bottom structure,said bottom structure comprising:

a central dome portion terminating in a circular bottom edge;

a semi-torus shaped rim portion circumscribing said central portion andconvexed downwardly from said container and having an outer marginaledge portion merging into said side wall and having an inner marginaledge portion merging with said dome portion at said circular edge; and

a plurality of shallow ribs formed in said rim portion of transversearcuate contour and intervening radially extending leg portions, eachrib portion having a relatively thick ridge section and having sidesections progressively thinned outwardly and merging into respective legportions.

2. The invention according to claim 1 and said dome portion disposed forloading in compression and said ribs disposed for loading in bend.

3. The invention according to claim 2 and said ribs having maximum widthin the area of juncture of the rim to the side wall and narrowing andshallowing at their outer and inner extremities.

4. The invention according to claim 3 and said by portions having narrowinner sections and broadening from said inner sections to relativelywide outer sections in the area of juncture with the side wall.

5. The invention according to claim 1 and said bottom structure having adiametric seam centered on diametrically disposed ribs.

6. In a plastic container formed of material adapted to deform whensubjected to predetermined pressure loads, said container having acylindrical lower side wall portion, an integral bottom defined by awall comprising an inwardly convexed sperical center portion, areversely convexed rim portion extending between said inwardly convexedcenter portion and said side wall and projective axially of thecontainer below the lowermost edge of said center portion, and aplurality of reinforcing elements formed as an integral part of said rimportion and extending radially of the container and having inner endsmerging into said center portion and flaring therefrom outwardly andbeyond the juncture of the bottom wall with the side wall narrowingcircum ferentially of the container and flaring into said side wall, andsaid reinforcing elements defining a plurality of legs oriented radiallyof the container and having wide circumferential sections adjacent tosaid side wall and narrow inner end sections at said center portion, andsaid reinforcing elements having lateral side segments of relativelythin cross section in their regions of merger with respective legs andforming the sides thereof and progressively being thicker axiallyinwardly of the container and merging into a relatively thick arcuateinner crest portion.

7. The invention according to claim 6 and said elements blending attheir ends into the side wall portion and said spherical portionrespectively.

8. The invention according to claim 7 and said legs being essentiallyU-shaped in radial cross-section.

* II 1h

1. A blow molded pressure resistant plastic container having a bodycomprising a generally cylindrical side wall and a bottom structure,said bottom structure comprising: a central dome portion terminating ina circular bottom edge; a semi-torus shaped rim portion circumscribingsaid central portion and convexed downwardly from said container andhaving an outer marginal edge portion merging into said side wall andhaving an inner marginal edge portion merging with said dome portion atsaid circular edge; and a plurality of shallow ribs formed in said rimportion of transverse arcuate contour and intervening radially extendingleg portions, each rib portion having a relatively thick ridge sectionand having side sections progressively thinned outwardly and merginginto respective leg portions.
 2. The invention according to claim 1 andsaid dome portion disposed for loading in compression and said ribsdisposed for loading in bend.
 3. The invention according to claim 2 andsaid ribs having maximum width in the area of juncture of the rim to theside wall and narrowing and shallowing at their outer and innerextremities.
 4. The invention according to claim 3 and said by portionshaving narrow inner sections and broadening from said inner sections torelatively wide outer sections in the area of juncture with the sidewall.
 5. The invention according to claim 1 and said bottom structurehaving a diametric seam centered on diametrically disposed ribs.
 6. In aplastic container formed of material adapted to deform when subjected topredetermined pressure loads, said container having a cylindrical lowerside wall portion, an integral bottom defined by a wall comprising aninwardly convexed sperical center portion, a reversely convexed rimportion extending between said inwardly convexed center portion and saidside wall and projective axially of the container below the lowermostedge of said center portion, and a plurality of reinforcing elementsformed as an integral part of said rim portion and extending radially ofthe container and having inner ends merging into said center portion andflaring therefrom outwardly and beyond the juncture of the bottom wallwith the side wall narrowing circumferentially of the container andflaring into said side wall, and said reinforcing elements defining aplurality of legs oriented radially of the container and having widecircumferential sections adjacent to said side wall and narrow inner endsections at said center portion, and said reinforcing elements havinglateral side segments of relatively thin cross section in their regionsof merger with respective legs and forming the sides thereof andprogressively being thicker axially inwardly of the container andmerging into a relatively thick arcuate inner crest portion.
 7. Theinvention according to claim 6 and said elements blending at their endsinto the side wall portion and said spherical portion respectively. 8.The invention according to claim 7 and said legs being essentiallyU-shaped in radial cross-section.